In the semiconductor arts, semiconductor wafers or substrates are processed in individual chambers which are generally part of a larger cluster platform having multiple chambers. FIG. 1 illustrates one such prior art process chamber 10. The process chamber 10 of FIG. 1 has a chamber housing 11, a chamber lid 14, a bottom shell portion 16, and a chuck 21.
The chamber lid 14 forms a seal with the chamber housing 11 either via a vacuum, fastening mechanism, or gravity to form a chamber 12 within the process chamber 10. The chamber housing 11 has at least one gas inlet 32 for introducing process gasses to the chamber 12, as well as a pumping ring 18 for evacuation of gas from the chamber 12 to the bottom shell 16 area. It is understood that the pumping ring 18 may be a removable baffle (not shown) that interfaces to an evacuation port in the chamber housing 11 for providing uniform evacuation of gases from the chamber 12. The chuck 21 includes a chuck support 22 which houses chuck controls 42 for providing mechanical, thermal, and power control to the chuck 21. Surrounding the chuck support is the bottom shell 16 which provides a pumping port 39 for evacuation of gasses from the process chamber 10. In addition, a liner 20 encircles the chamber 12 within the chamber housing 11, and will be discussed in more detail below.
In operation, a semiconductor substrate 30 is placed upon the chuck 21 by an automated mechanism such as a robotic arm. The semiconductor substrate 30 is generally introduced through an opening in the chamber 12 (not shown). The chamber lid 14 is sealed to the chamber 12 in order to form the enclosed portion of the chamber 12.
In order to assure that the material forming the inner wall of the chamber 12 does not react with the processing of the semiconductor substrate 30, a liner 20 encircles the chamber 12 on an inner surface of chamber housing 11. This liner 20 isolates the processing area of the chamber 12 that would be exposed to plasma 33 from the material comprising the chamber housing 11 to assure that an undesirable reaction does not occur during the semiconductor substrate processing. The liner 20 is a removable liner made of plastic composite materials such as polycarbonates. One of the attributes considered in choosing liner 20 is its ability to adhere to polymers created in the plasma 33. This adhesion is facilitated based on the relatively rough surface of the liner as well as the fact it is an insulator which provides a non-powered, and cooler surface. As the polymer adheres to the liner, particles can be trapped within the polymer on the liner.
During the processing steps associated with the manufacture of semiconductor substrates 30, gas is introduced through the gas port 32, and the ionization of the gases produces a plasma 33 in the chamber area 12. The plasma 33 is excited via a plasma power supply (not shown) in order to produce plasma 33 and react in a desired manner with a semiconductor substrate 32. During the plasma process, particles 35 are produced in the chamber area 12. In addition, these particles can be introduced from a number of sources, including the wafer transport system, such as the mechanics which introduce the semiconductor substrate 30 into the chamber, as well as particles introduced inadvertently with the gas stream through gas ports 32.
The particles 35 become suspended in the plasma 33 above the semiconductor substrate 30 surface due to electrostatic interactions. During processing procedures while power is applied, the particles 35 do not generally cause processing problems, as they are typically suspended above the semiconductor substrate. However, as the power is reduced at the end of a processing cycle, the forces that suspend the particles 35 dissipate allowing them to fall out of the plasma 33 and land upon the semiconductor substrate surface 30 causing contamination. The falling action can be the result of both gravity and electrostatic attraction to the semiconductor substrate 30.
In order to reduce the effects of this contamination, the prior art relies on a polymer film being formed during processing to trap particles 35. These trapped polymers form a film over the lining which over time builds and needs to be physically removed as discussed below. In addition, during a post-process venting step, the liner 20 in combination with the polymer film trap particles 35 only when physical contact occurs. Other prior art steps to reduce particle contamination include the use of a pump purge cycle. A pump purge cycle is used after the processing of the substrate 30 by introducing an inert gas to the process chamber 10 to generate a pressure greater that would normally be experienced during processing. Once this pre-defined pressure is reached, the pump port is opened to allow rapid removal of the introduced gas. This rapid removal creates turbulence which has a sweeping effect carrying particles with the escaping exhaust gasses 40 outside the process chamber 12. A disadvantage of the pump purge cycle is that the pump purge cycle attempts to overcome the static forces affecting a particle with a mechanical force, as a result, the static on the particle is still available to attract the particle to a different undesirable location in the chamber 12. Therefore, a pressure purge does not necessarily remove the contaminants, but only redistributes them.
Another prior art method to assist removal of particles is to physically agitate the chuck 21 to loosen or remove fallen particles. This allows the pump purge mechanisms to better remove the contaminants. The agitation of the chuck can occur during the latter stages of the power cycle or the ramp down cycle, where the plasma energy is being reduced. Performing the agitation of the chuck 21 while the plasma energy is still present facilitates removal of the particles from the substrate surface by a combination of physical and electrostatic forces. A disadvantage of this prior art technique is that while the particle may be removed from the substrate 30, these may not be efficiently removed from the process chamber as the particles are be attracted to other surfaces causing the potential for continued contamination.
Yet another prior art method to assist removal of particles is to change the plasma chemistry, by introducing other gasses, during the latter stages of the substrate 30 processing, or as a separate step. By doing so, the electrostatic nature of the particle is changed such that it is less likely to adhere to various surfaces, allowing for more efficient removal during a pump purge cycle. A disadvantage of this step is that additional gasses require additional total processing time to accommodate the introduction of the new gasses. In addition, the use of this prior step, while reducing the static charge on particles, does not completely physically remove the particles from above the substrate 30.
A further disadvantage of the prior art method is the need to replace or physically clean the liner 20 because of the polymer film build-up. This is required because the polymer film with trapped particles will flake and peel over time introducing additional contaminants to the chamber environment 12. This relatively frequent replacement or cleaning of the liner 20 requires significant and costly down time during which the process chamber 10 cannot be utilized.
The need for an apparatus and method that would allow for improved removal of particles from a processing chamber and substrate surface during a processing cycle without adding significant time to the cycle is desirable. This is especially true as the feature dimensions of devices on the semiconductor substrate decrease, the particles size that become a concern also decreases. Generally, a particle one-third the size of the minimum geometry of a semiconductor substrate feature can cause device defects. As the particles' size decreases, the relative proportion of these particles generally geometrically increases.